Chiral Analysis of Re-crystallized Mixtures of D-, L-amino Acid Using Terahertz Spectroscopy
Distinguishability by terahertz absorption between D- and L-amino acids and a change in terahertz absorption based on the re-crystallization condition was examined. Terahertz spectra which were obtained from the re-crystallized each enantiomer or mixtures of D- and L-leucine or alanine were compared with those of the purchased reagents. The peak tops of the re-crystallized L- and Dleucine mixtures were shifted toward low frequency side and the half width of the peak at 3.7 THz became narrow to approximately half of that of the reagent. Difference of spectral features from 2.1 THz to 2.8 THz in the THz spectra between D- and L-alanines was observed. According to the result of peak separation against these spectra, distinction between the purchased D- and L-alanine was possible to compare the intensities of the sub-peaks. Moreover, changes of the integrated values of the peaks obtained from L- or D-form-rich mixture of leucine were observed. These results suggested that feasibility of chiral analysis of enantiomers using terahertz spectroscopy would be shown.